It meant Ferdinand was indeed just a child, someone akin to a toddler or even younger when he met Ellie since he could not even take human form.
And when Ferdinand began to raise the second generation of dragons, he was akin to just 15-16 years old even though he was already an ancient creation back then when judged by humans.
After Ferdinand explained to her, Arabella decided to tell him the real reason why Eliana left his side. Perhaps it was because Eliana's soul was hers now, Arabella didn't want the misunderstanding to remain as it was.
"Eliana did not leave you because she thought you couldn't sire a child. It was because she loved you so much that she decided to let go when she thought you didn't want her by your side the way she does."
